1. Field of the Invention
This invention concerns methods and equipment for switching a tape-recorder which operates with magnetic tape to be wound on a reel and, at the same time, drawn off the same or off another reel, the magnetic tape being attachable to the reel or reels and the tape surface being scanned to effect the switching operation.
The invention also concerns methods and equipment for switching a tape-recorder capable of operating with tape coated with different types of magnetic layer which may be provided with a leader and/or a trailer, at least one switching state of the recorder being achievable by continuous or sporadic scanning of the tape surface.
2. The Prior Art
A device for triggering a signal for controlling the drive mechanism of a tape-recorder is known, especially for disconnection when the tape end is reached. In this known arrangement, a reproduction head cooperating with a special recording on the tape, at least one amplifier stage, a demodulator and a fixed-threshold amplitude comparator stage (the threshold must be higher than the noise voltage of the amplifier stages and lower than the noise voltage of the magnetic tape) are needed to produce the control signal when the scanned level falls below the threshold level. This arrangement relies on the condition that the noise signal at the reproduction amplifier output drops by 10 to 12 dB when the leader tape is scanned. By selectively limiting the frequency band of the output voltage of the reproduction amplifier, the control signal is to be triggered after amplification, amplitude limitation, demodulation and amplitude comparison.
In view of the multitude of additional stages all of which have to be matched comparatively accurately, the known methods and the equipment necessary to carry them out are hardly justifiable economically.
In particular, with recordings on low-noise tape extremely low noise voltages at the reproduction amplifier output are required if the ratio to the tape noise voltage required for the safe functioning of the arrangement (10 to 12 dB) is to be preserved.
According to the German Industrial Standard DIN 45512, leaders used for magnetic tape of 6.3 mm width consist of a coloured tape of synthetic material 1 m long and a highly conductive switching section of 15 cm length on which the resistance of the conductive layer is equal to or less than 2.5 ohms, the switching section being spliced to the magnetic tape. As the end of the magnetic tape travels past, an electric circuit is closed by means of the switching section and two contacts touching the tape, and the tape-recorder is switched off by means of relays or other switching devices, so that the end portion of the tape cannot run off and the user is obliged to re-thread the tape prior to re-winding. The particular disadvantage of this type of leader or trailer for the purpose of tape end switching is the additional expense in manufacture.
In the case of tapes for small cassette recorders, no special switching sections or adhesive reflector markers etc. are used for economy reasons. Here, the leader merely consists of a non-coated transparent synthetic tape of great strength which is attached to the reel core (see, for example, DIN 45 516). This kind of synthetic tape has so far not been used for switching purposes, except optically.
Other arrangements for switching tape or cassette recorders monitor the tape tension, the centrifugal force or the rotation of the take-up spindle to produce a control signal. According to another known method, switching operations are triggered by the photoelectric scanning of holes punched, or transparent tape sections inserted, in the magnetic tape.
Another tape-recorder switching device is known in the case of which the ferro-magnetic surface of the tape-like recording medium is scanned to trigger a switching operation. Here, the tape is rendered less conductive or completely insulating at its ends. During scanning, the resistance of the recording medium is continuously monitored and a definite state is allocated to each of the two different resistance values: the state "machine operative" is allocated to the highly conductive surface (resistance a few ohms) of the recording medium, and the state "machine stops" is allocated to the less conductive surface (resistance virtually infinite at the ends of the recording medium). This known arrangement can only be employed for the on/off switching of the tape recorder.
However, all the above-described arrangements are technically complex without exception, and accurate switching operations cannot be controlled with sufficient reliability.
Also known are tape recorders on which tape coated with different types of magnetic layer can be used. Such magnetic tapes are, for example iron oxide tapes (Fe.sub.2 O.sub.3), chromium dioxide tapes (CrO.sub.2) and metal pigment tapes.
CrO.sub.2 tapes and metal pigment tapes are characterized by a remanent flux higher than in comparable Fe.sub.2 O.sub.3 tapes and also by a more favorable remanent flux/sound or other wavelength characteristic, especially in the low wavelength spectrum. In order to derive the full benefits from CrO.sub.2 tapes, the tape-recorder has to be adapted to the improved magnetic properties of these tapes by switching the recorder electronics prior to using CrO.sub.2 tapes. Thus, in view of the higher coercivity of the CrO.sub.2 tapes, an HF magnetising current and an erasing current must be set which is higher than in the case of Fe.sub.2 O.sub.3 tapes, in order to achieve optimum recording and erasion. The favorable tape flux characteristic of low wavelengths makes it possible to work with less highly raised high-frequency signal amplitudes in the reproduction amplifier, and this has a beneficial effect on the signal-to-noise ratio of the recorder.
To enable such switching operations to be effected, cassette recorders have been devised which operate with specially modified cassettes. The modifications consist of apertures or metal foils on the cassette housing which cooperate with corresponding switching devices on the machine and thus trigger switching operations. The modified-cassette idea has the disadvantage that additional operations become necessary during cassette manufacture. Moreover, these switching arrangements cannot be used for ordinary tape recorders operating with reels.
The switching of the tape-recorder electronics in dependence on the type of tape employed has so far not been found possible without expensive additional markings directly on the tape or on a cassette.